In a type of masonry wall construction for buildings, known as cavity wall construction, a structural back-up wall of concrete block, structural clay tile units, poured concrete, or wood or steel framing with attached sheathing material, is spaced from the structure's exterior masonry wall consisting of brick or other unit masonry. The cavity or space between the structural back-up wall and exterior masonry wall is typically from 1–4 inches. In cavity wall construction, it is important to remove water and water vapor in the cavity in order to prevent damage to materials of the walls and to maintain the strength and appearance of the walls. Water and water vapor can be present in the cavity for a number of reasons, including condensation of moisture in the air, migration of water and water vapor through the exterior masonry wall, cracks and other openings in the exterior masonry wall, water leaks in the roof or elsewhere in the building, water and water vapor migrating from the building interior through the structural back-up wall, and various other reasons. Water and water vapor in the cavity is usually an on-going condition which cannot always be eliminated. The presence of water or water vapor can cause degradation of the construction materials of the exterior masonry wall, the structural back-up wall, or even the foundation. If not controlled during freezing conditions, serious damage can occur. The presence of water and water vapor can migrate to the interior and promote the growth of mold,  and can migrate through the exterior masonry wall forming an unsightly deposit of salts or efflorescence on the exterior face of the wall, or unsightly streaks from the corrosion of metal building components associated with the walls.
Water vapor can be removed or reduced in the cavity with use of vents from the cavity through the exterior masonry wall to the outside air. The vents are preferably located both near the top and bottom of the wall so as to promote air currents through the cavity. Water can be removed or reduced in the cavity by a weep system at the base of the cavity for removing water which makes its way to that location. In a weep system, openings are provided through the exterior wall to transport the water to the outside.
Although a weep system can work well, it is often prevented from working as designed due to the presence of “trash mortar” which drops into the cavity and generally collects at the bottom of the cavity during construction of the exterior masonry wall. The amount of trash mortar collected at the bottom can vary greatly depending on the height of the exterior masonry wall, the masonry unit installation technique employed by the mason, the consistency of the mortar, working conditions, etc. The trash mortar can block the openings of a cavity weep system and vents and impede the removal of the water and water vapor.
Various systems have been developed for preventing trash mortar from dropping to the base of the walls. One system, found in U.S. Pat. No. 5,598,673, incorporates a coarse polymer mesh material for substantially filling the cavity and preventing the mortar from falling to the bottom of the cavity. It must be installed to the exterior face of the structural back-up wall prior to laying-up the exterior masonry wall. The system requires a significant added construction step and somewhat restricts the free-flow of air in the cavity after installation. Moisture condensing in the cavity, or water otherwise present in the cavity, is presented with a  torturous route in order to reach a cavity weep system at the base of the walls, thus delaying its removal. The coarse polymer mesh material, which makes contact with both walls, can hold water moisture at contact points on the surfaces of the walls facing the cavity, thus subjecting the material of the walls to water and water vapor over long periods of time.
U.S. Pat. Nos. Re. 36,676, 5,230,189 and 5,343,661 describe a water-permeable material which is generally placed at the bottom of the cavity. As in the previous device the material makes contact with the walls and condensed water, or water otherwise found on the water permeable material, eventually makes its way to the weep system at the base of the walls. This method is effective in holding mortar above the bottom of the cavity, however it does present limitations, in that, although it collects trash mortar on the top surface of the mesh material at various elevations, it does not prevent the mortar from simultaneously touching the inside of the masonry wall and the face of the structural back-up wall, resulting in a condition referred to as “bridging”. The bridging mortar can provide a route for water to travel from the inside of the exterior wall to the structural back-up wall. Also, although it collects trash mortar on the top surface of the mesh material at various elevations, it does not prevent an uncontrolled amount of excessive mortar from building up to the point where the flow of water and air is inhibited.
A system described in U.S. Pat. No. 4,282,691 features a device for allowing the escape of water from a wall cavity by providing an exit through the exterior wall. The device includes a tube having a water outlet and an inlet, with an elongated porous wick material extending outwardly from the water inlet to absorb water and water vapor. In operation, water seeps from the wick end to the outlet end. A plurality of tubes are inserted through the exterior wall near the base of the walls. The system does not provide a means for preventing trash mortar  from dropping from upper levels to the base of the walls and therefore proper operation of the device can be impeded by the presence of the mortar.
Another system, U.S. Pat. No. 5,845,455, uses an elongated sheet collecting device positioned in the cavity and attached to the masonry ties to prevent mortar from accumulating in the bottom of the cavity and blocking weep holes. This method is effective in holding mortar above the bottom of the cavity, however it does present limitations. It can only be used in conjunction with a limited number of masonry tie systems, and although it collects trash mortar, it does not prevent that mortar from bridging across the cavity, which could provide a route for water on the inside of the exterior wall to travel to the structural back-up wall.
It is an object of the present invention to provide a device for preventing trash mortar, in cavity wall construction, from dropping to the base of the masonry wall, primarily during the construction phase of a building and not allowing that mortar, which it collects, to bridge across the cavity, and to provide a means for promoting rapid removal of water and water vapor in the cavity during the life of the structure.
It is a further object of the present invention to provide a device for promoting transfer of water in the cavity to a base weep system in a minimum amount of time and directing the water away from the surfaces of the walls which face the cavity.
It is yet a further object of the present invention to provide a device which does not require a significant added construction step or significant deviation from conventional construction procedures and conventional tie devices used by masonry tradesmen.
It is yet a further object of the present invention to provide a device which does not result in the bridging of mortar between the walls. 